if youre asking why it's red, not 100% sure atm. It's currently rebuilding, thought it might be related to your patch that you sent to br-dev last night. if that's not it, I'll try updating the ybd it uses

The syntax is intuitive for most mathematical operations. There are several compilers. If you lack batteries, use mains. My (limited) experience with APL is that doing the same thing gets the same result, which seems sane.